Arthur C. Clarke famously said that "Any sufficiently advanced technology is indistinguishable from magic." I always keep this quote in my mind when reading science fiction and try to spot where things become indistinguishable from magic. They always do. One of the most popular ways in modern sci-fi to get away with magic is to invoke nanotechnology. It seems that if you just wave your hands and say "nanobots" you can get away with anything!

With that in mind, I thought it would be interesting to take a look at some real-world nanotechnology. What is actually plausible and what is still truly magic?

First let's get this out of the way: I don't think we're going to see swarms of tiny robots doing our bidding (or reducing the world to a seething gray goo) any time soon. The reason? Well, aside from the fact that it's just really hard to build things so tiny, and even harder to tell them what to do and how to do it, there's the minor fact that we already live in a world crawling with molecular machines of such stunning precision and elegance that we will never be able to do better. Turns out that instead of a doomsday scenario of gray goo, a planet-enveloping swarm of fully-functioning microscopic self-replicating entities leads to the spectacular and rich biological ecosystems we see all around (and in) us.

Instead of nanobots, some of the most successful applications of nanotechnology are actually in designing new materials at the molecular level. It turns out that you can get some really startlingly cool materials when you have great control over their molecular structure. Even within the subfield of nanomaterials there is a lot to cover, so I decided to focus on two types of nanomaterial in particular: aerogels and carbon nanomaterials.

Aerogel is the least dense solid substance known – the record-holding aerogel has a density of 1.9 milligrams per cubic centimeter. That's just slightly more than the density of air! The most common aerogels are made of silica particles that are put into suspension in a liquid and allowed to form a gel. Then the liquid is removed, leaving an airy structure of nanometer-sized silica spherules bonded together into branching fractal chains. Even though silica aerogels are the most common, other materials such as carbon, aluminum oxide and various metals have also been used.

Because of their extremely low density, aerogels are almost perfect insulators, so as they become more affordable to produce they are making their way into extreme cold-weather clothes and blankets and thin slabs of transparent aerogel are being used in windows. NASA loves the stuff: it has used aerogel to capture dust grains from a comet in the Stardust mission, and as insulation on the Mars rovers and in space suits. Aerogel also has some very useful chemical properties: since it has an enormous surface area, it can be used to absorb chemicals such as heavy metals very efficiently, making it great for cleaning up pollution. Its surface area also makes it useful as a catalyst for chemical reactions, such as in fuel cells.

Another class of nanomaterials with a seemingly endless list of useful properties are carbon allotropes. Picture chicken wire made of individual carbon atoms bonded together. This mesh of carbon is graphene, a molecule 200 times stronger than steel yet transparent and electrically conductive. It was originally isolated by using scotch tape to remove single layers of carbon atoms from graphite, but in the last few years scientists have finally figured out to produce large sheets of graphene, and the 2010 Nobel prize in physics went to researchers studying this amazing macromolecule. As it gets easier to produce and manipulate, you can expect to see graphene making an appearance in everything from touchscreens and compact electronics to high-strength composite materials and solar panels.

But graphene is just the beginning. Take these sheets of carbon and roll them up and you get carbon nanotubes. These tiny cylinders of carbon have the highest tensile strength of any material known, are harder than diamond, and as of 2010 can be up to 18 cm long. And of course they conduct electricity just like their relative graphene.

Sci-fi readers are probably most familiar with nanotubes as the key component in building a functioning space elevator: their extreme tensile strength for their weight makes them ideally suited for the ultra-strong cable that would be necessary. But nanotubes have more uses than just building long, strong cables. In fact, they may have been used thousands of years ago, before anyone knew about atoms or molecules, let alone nanomaterials! Anyone who knows a bit about swords has probably heard of the famous "Damascus steel" that caused the Crusaders such grief. Well, it turns out that the alloy Damascus swords are made of – called "wootz" and originating in India – might actually contain nanotubes grown when impurities in the ore catalyzed the growth of carbon from smoke in the forges.

But fancy swords and space elevators aside, there are an almost endless list of modern uses for carbon nanotubes. For instance: bulletproof t-shirts. Mats of nanotubes have been made into incredibly strong and thin sheets. A stack of 100 sheets, about a millimeter thick, can stop a bullet. That doesn't mean that if you're wearing nanotube fabric being shot won't hurt, but it stops the bullet and that's not bad for such a thin fabric!

Another surprising use for carbon nanotubes is in paper batteries. That's right, by combining carbon nanotubes and cellulose fibers like those in normal paper, researchers have created a material that stores energy like a battery but looks and feels like black paper. The nanocomposite paper batteries store energy at temperatures ranging from -100 to 300 degrees Fahrenheit – much better than typical batteries – and work if they have been folded, rolled or even cut!

Carbon nanotubes might even be used as artificial muscles! Nanotube muscles are actually based on carbon nanotube aerogels, and can expand to three times their original size in one direction when a voltage is applied, and then shrink back to their original size when the voltage is released. By combining the lightweight properties of aerogel and the electrical properties and great strength of carbon nanotubes, these synthetic muscles could be ideal for space exploration, where weight and energy are at a premium and temperatures can be far too hot or too cold for other synthetic muscles or more traditional mechanical systems to work. So far, nanotube muscles require too high a voltage to be practical for human prosthetics, but that's a pretty minor detail for sci-fi.

Of course, it's impossible to cover all of the awesome new materials that are the result of nanotechnology research, but I hope I've made it clear that even if swarms of nanobots are not likely, there are some really amazing developments coming out of nanotechnology research. There's plenty of material that is ripe for the science fictional picking without resorting to clichéd nanobots. And even though things like paper batteries or artificial muscles or bulletproof t-shirts sound suspiciously like technology that is advanced enough that it is "indistinguishable from magic", they already exist and even more exciting applications are right around the corner.

Now, let's get to work on that space elevator.

Image: Aerogel is an almost perfect insulator. Here a thin slab of aerogel is able to protect a box of matches from a blowtorch! Photo: NASA/JPL. This post first appeared on Science In My Fiction.